Autonomous computer-aided surgical systems generally consist of a robotic arm attached to a base. The robotic arm performs a set of instructions created either pre-operatively or intra-operatively to aid the user in performing a particular medical procedure. One such system is the ROBODOC™ Surgical System (THINK Surgical, Fremont, Calif.) that aids a user in precisely milling the cavity of a femur to receive an implant in total hip arthroplasty (THA). As shown in FIGS. 1A and 1B the ROBODOC™ Surgical System 101 generally consists of a robotic base 103, a robotic arm consisting of various links and joints 105, a tool 107 having a tool tip 108, and a digitizer 109. The digitizer 109 is a passive mechanical arm having a digitizer probe with a probe tip 110. The digitizer 109 is used to collect a set of points on a bone to register the bone coordinate frame with the robots coordinate frame.
In order to ensure that a bone cavity is created with sub-millimeter accuracy, the robotic arm, digitizer 109, and tools all need to be within tight operating parameters. Generally, the robotic arm and digitizer 109 are calibrated by the manufacturer when first installed at a customer's site. The kinematic parameters are updated to account for any errors including joint-level errors, kinematic modelling errors, and non-geometric errors. Subsequently, prior to each medical procedure, the calibration is verified to ensure the accuracy of the system.
Many different external measuring devices and methods are used to calibrate or verify the calibration of a robotic arm including touching the tool tip to reference parts, laser triangulation, and calipers. As many of these techniques have been employed on industrial robots, their use in computer-aided surgical systems is limited due to the surgical setting and strict regulatory requirements. For example, the ROBODOC™ Surgical System utilizes a reference plate. The reference plate has multiple reference points that are spaced a known distance apart within very tight tolerances. The tool tip 108 and digitizer tip 109 are guided to the center of each of the reference points. The position of the digitizer tip 110 and tool tip 108 is recorded at each of these reference points using the kinematics (e.g., Denavit-Hartenberg (DH) parameters, encoder values) of the digitizer 109 or robot 101. If the difference between the known locations of the reference points is within a specified tolerance of what is measured by the kinematics, then the calibration of the robot and digitizer is verified. The procedural steps are often time consuming and require additional hardware (i.e., reference parts, calibration probes, optical tracking systems) that can further increase costs. Additionally, when verifying calibration prior to surgery, the external measuring tools must be sterile; this results in increased disposables and/or sterilization considerations.
Additionally, surgical systems often require maintenance and tuning to ensure the operating parameters are functioning properly. However, maintenance is usually only performed at designated time intervals or when there is a noticeable error or system malfunction.
Thus there exists a need in computer-aided surgical systems for a quick method to calibrate and verify the robot and robotic tools are calibrated. There further exists a need to maintain the sterile environment during calibration verification. There is an even further need to provide feedback to a user when to tune or provide maintenance to a surgical system prior to a malfunction